Differentiation induces a change in microtubule organization in cell types as diverse as epithelia, muscles and neurons. This requires loss of the centrosome's microtubule organizing activity and formation of non- centrosomal microtubule arrays. We have a very limited understanding of how this reorganization occurs and the functions of the resulting microtubules. In part, this is due to lack of tools to observe and specifically perturb microtubule organization in tissues. The long-term goal of our work is to understand how diverse microtubule organizations are generated in differentiated cells and to expose their functions. The objectives of this proposal are to determine how loss of centrosomal organizing activity and microtubule minus end anchoring proteins collaborate to induce specific microtubule arrays. Based on our preliminary data, we hypothesize that differentiation causes changes in both nucleation and anchoring of microtubules at centrosomes. In combination with cytoplasmic minus end anchoring proteins, this allows for specific cytoskeletal structures to form in differentiated cells. We have developed tools/technologies that will allow us to fully characterize the changes in centrosome nucleation activity, ultrastructure and protein composition that occur upon differentiation in the epidermis. In addition, we will elucidate the underlying molecular mechanisms that lead to changes in centrosome composition and activity. Finally, we have developed novel mouse lines that will be used to examine the roles of noncentrosomal microtubule arrays in both the skin and the intestine through specific disruption of microtubule minus end anchoring proteins. These studies will elucidate the mechanisms regulating centrosome activity and microtubule reorganization in differentiated cells and determine the physiologic functions of these arrays in two different tissues.